fix(highlight.run): correct privacy masking for empty strings (#332)

## Summary

Brings in launchdarkly/rrweb#6 to correct
privacy masking for empty strings.

## How did you test this change?

<img width="3537" height="1946" alt="image"
src="https://github.com/user-attachments/assets/be3d2e66-0c91-42a6-b74a-d72c3cd3909d"
/>


## Are there any deployment considerations?

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 Backend - Do we need to consider migrations or backfilling data?
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<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Adds an extra `ld-mask-text` block in the privacy demo to cover short
words and multiple spaces.
> 
> - **E2E React Router Privacy Demo**
> - Update `e2e/react-router/src/routes/privacy-demo.tsx` to include a
new `ld-mask-text` `<div>` with text containing short words and extra
spaces for masking behavior coverage.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
fd30057. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

---------

Co-authored-by: SpennyNDaJets <samarantides@launchdarkly.com>

Author: Vadman97

e2e/react-router/src/routes/privacy-demo.tsx

@@ -42,6 +42,10 @@ export default function PrivacyDemo() {
 				<p className="ld-mask-text">
 					<span>Secret text</span>
 				</p>
+				<div className="ld-mask-text">
+					Test a string with shorter words like in and with extra
+					{'    '}spaces.
+				</div>
 			</section>
 
 			<section>